Printed conductive films have the potential to lower manufacturing costs for microelectronics and large area electronics. Recently, metal nanoparticles having consistent size and shape have been developed. These nanoparticles may be used to prepare well-dispersed inks. These metallic ink dispersions may be used for printing conductors, thereby making the direct writing of electronic circuits possible. Silver and gold nanoparticle-based inks are beginning to be used for printing electronics. These metals are used because of their relatively high stabilities toward oxidation by molecular oxygen. Copper also has been extensively used for electronics and microelectronic chips. Although copper is less costly than silver or gold, oxidation of copper nanoparticles during printing and curing limits its usefulness.
Conductive inks are mainly classified into firing type conductive inks and polymer type conductive inks. The firing type conductive inks develop conductivity by heating to about 200 to 400° C., and thereby metal particles are sintered to each other and a continuous conductive layer can be obtained. However, adhesion to substrates is poor. The polymer type conductive inks contain resin that improves adhesion to a substrate. When the resin in the polymer type conductive ink cures the metal particles simultaneously contact each other and a conductive film is formed.
However, cured resin is an insulating material and intervenes between the metal particles. Consequently, the resultant film has relatively poor electrical conductivity. Indeed even the best silver-based conductive epoxies exhibit conductivities that are several orders of magnitude smaller than pure silver.
Therefore, it would be desirable to develop electroconductive ink that has excellent electrical conductivity such as obtained with sintered metal nanoparticles along with excellent adhesion to the substrate to which the ink is applied.